1. Field of Invention
The present invention relates to a thermal-resistance material, and more particularly to a multi metal base thermal resistance alloy and a mold with the multi metal base thermal resistance alloy layer.
2. Related Art
With the development of the global communication industry, there has been an increasing demand for portable devices such as notebooks (NBs) and cellular phones, which must meet design requirements of being light and small. Taking the notebook for example, conventionally, the housing of the notebook is mainly made of engineering plastics (ABS). However, Mg alloy can be used instead of ABS, and Mg alloy has the advantages of higher density and significantly increased Young's modulus (GPa), as shown in the following table. Besides, Mg alloy further has the environmental protection features of being heat dissipative, electromagnetically shielding, and recyclable.
Density (g/cm3)Young's modulus (GPa)ABS1.072.1Mg alloy1.81445
However, Mg alloy is manufactured by a process of die casting, which easily results in defects on the surface of the casting, with defect rates of up to about 50%. On the other hand, Taiwan is the first in the world in the capacity of manufacturing devices for die casting Mg alloys of NB, but the yields are poor, which is the main bottleneck for productivity. The die casting of Mg alloys faces many defects, with primary causes including that the casting is relatively thin in size; the heat dissipating process is too fast when the metal is solidified; and non-directional solidification occurs. Due to fast heat effusion when the metal is solidified, defects at semi-solid molding include: incomplete thermal shrinking and filling . . . ; defects at Mg alloy die casting include: hot split film, surface oxidation, streaks, surface holes, and outstanding deformation.
Therefore, if a thermal-resistance material is sprayed and coated onto the surface of the Mg-alloy die casting mold (SKD61) or the semi-solid mold as a heat insulating coating, that the heat effusion process will be slowed down when the Mg-alloy die casting mold or the semi-solid mold is solidified, thereby improving the solidification compensation, which conforms to the above-mentioned metal solidification theory.
During the research of thermal-resistance materials with low thermal conductivity coefficients, most thermal-resistance materials are ceramic matrix composites. Currently, thermal-resistance materials have always been used in high-temperature environments, such as turbine blades or their parts. Turbine bladed or their parts are often made of superalloys. Although the material of superalloy is high temperature-resistant, it also faces the problems of being fatigued and destroyed due to being used for a long time. At present, the most common solution is cladding a thermal-resistance material on the surface of the turbine blade or its parts. ZrO2 is the earliest oxide to be used as a thermal-resistance material. With the development of ZrO2 as a thermal-resistance material, many researchers began devoting themselves to developing various ZrO2-based thermal-resistance materials.
At present, the most commonly used thermal-resistance material is Yttria-Stabilized Zirconia (YSZ). To further reduce the thermal conductivity coefficient, some researchers have added other oxides into YSZ, for example, Nb2O5 is added into YSZ in U.S. Pat. No. 6,686,060.
In U.S. Pat. No. 6,764,779, a 6-8 wt % (weight percent) YSZ layer and an 18-22 wt % YSZ layer are stacked with each other, to reduce the thermal conductivity coefficient. Additionally, other researchers add other oxides into ZrO2. For example, in U.S. Pat. No. 6,284,323, 5-60 mol % Gd2O3 is added into ZrO2; in U.S. Pat. No. 6,916,551, Er2O3 is added into ZrO2; both ways can obtain a thermal-resistance material with a low thermal conductivity coefficient.
Furthermore, other researchers have developed other new oxides to replace ZrO2, for example, in U.S. Pat. No. 6,924,040, Gd2O3 is added into HfO2, and similarly equivalent low thermal conductivity coefficient can be achieved.
In U.S. Pat. No. 6,803,135, RexZr1-xOy (0<x<0.5, 1.75<y<2) acts as the thermal-resistance material cladding on the metal substrate. Re (rhenium) is a rare element on earth, and the rare elements include Ce, Pr, Nd, Pm, Sm, Eu, Th, Dy, Ho, Er, Tm, Yb, and Lu.
In addition to the thermal-resistance material of oxides, in U.S. Pat. No. 6,521,353, a few Mn and Cr are further added into the combination of 50-80 wt % WC and 10 wt % TiC+Co+Ni to produce a super-hard metal with a low thermal conductivity coefficient.
All of the above patents about thermal-resistance materials are directed to the ceramic matrix composites, especially those with oxide ceramic materials as the main portion. It can be easily known from the above thermal-resistance materials that quite a few rare elements are employed, and material costs will obviously increase.
In most of the patents, the composition of the one that disclosed in U.S. Pat. No. 6,756,131 includes Ni, Co (0.1-12 wt %), Cr (10-30 wt %), Al (4-15 wt %), Y (0.1-5 wt %), Re (0.5-10 wt %), Hf (0-0.7 wt %), and Si (0-1.5 wt %). Although pure metal elements are completely used for the thermal-resistance material of the alloy, quite a few rare elements still must be added into the material.